VirB10 for vaccination against gram negative bacteria

ABSTRACT

The invention pertains to the use of VirB10 to immunize a host against an infection by a bacterium having T4SS. The invention provides a vaccine comprising VirB10, a fragment of VirB10, a polynucleotide encoding VirB10 or a polynucleotide encoding a fragment of VirB10 and a pharmaceutically acceptable carrier and/or adjuvant. The invention also provides a method of immunizing a host against an infection caused by a bacterium having T4SS, the method comprising administering to the host a vaccine of the invention. The vaccines and the methods of the invention can be used to immunize against infections caused by bacteria having T4SS in dogs, rabbits, cats, pigs, cattle, sheep, goats, deer, horses, rodents and humans.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is the U.S. national stage application of International Patent Application No. PCT/US2016/037728, filed Jun. 16, 2016, which claims the benefit of U.S. Provisional Application Ser. No. 62/180,245, filed Jun. 16, 2015, the disclosures of which are hereby incorporated by reference in their entirety, including all figures, tables and amino acid or nucleic acid sequences.

This invention was made with government support under U54AI1057156 awarded by National Institutes of Health. The government has certain rights in the invention.

The Sequence Listing for this application is labeled “Seq-List.txt” which was created on Jun. 10, 2016 and is 343 KB. The entire content of the sequence listing are incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

Type 4 secretion system (T4SS) is used by many gram negative bacteria, including certain pathogenic bacteria, to secrete effector proteins and DNA across cell membranes. The bacteria belonging to the genus Rickettsia and Anaplasma provide examples of the pathogenic bacteria having T4SS. Rickettsial diseases are present worldwide and pose the threat of use in a biological weapon. Vaccines currently available against diseases mediated by the bacteria having T4SS are inadequate.

BRIEF SUMMARY OF THE INVENTION

T4SS is typically formed from a macromolecular complex of about 12 proteins. One of the proteins of T4SS is VirB10. The invention provides for the use of VirB10 to immunize against an infection by a bacterium having T4SS. Accordingly, the invention provides a vaccine comprising VirB10, a fragment of VirB10, a polynucleotide encoding VirB10 or a polynucleotide encoding a fragment of VirB10 and a pharmaceutically acceptable carrier and/or an adjuvant.

The invention also provides a method of immunizing a host against an infection caused by a bacterium having T4SS, the method comprising administering to the host a vaccine comprising or consisting of VirB10, a fragment of VirB10, a polynucleotide encoding VirB10 or a polynucleotide encoding a fragment of VirB10 and a pharmaceutically acceptable carrier and/or an adjuvant. The vaccines and the methods of the invention can be used to prevent infections caused by bacteria having T4SS in various hosts, for example, dogs, rabbits, cats, pigs, cattle, sheep, goats, deer, horses, rodents and humans.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A-1F. SDS-PAGE and Western Blot analysis of the recombinant proteins VirB9-1, VirB9-2 and VirB10. SDS-PAGE analysis of recombinant VirB9-1 (A), VirB9-2 (C), and VirB10 (E). Lanes represent the different fractions analyzed during the purification procedure, 1=Total crude protein, 2=Supernatant fraction obtained after high speed centrifugation, 3=Filtered supernatant, 4=Nickel Column filtrate, 5=Washed fraction, 6=Eluted protein, 7=Concentrated protein. Western Blot analysis using the monoclonal anti-His₆-tag antibody reacting with the recombinant protein (red arrows) VirB9-1 (33.5 KDa) (B), VirB9-2 (31.6 KDa) (D) and VirB10 (52.2 KDa) (F) in different fractions.

FIG. 2. A. phagocytophilum burden in mouse blood (different strains infected with HZ). A. phagocytophilum growth kinetics in blood were measured by determining GE/μ1 based on the single copy gene msp5. GE/μ1 calculations were normalized based on the volume of blood collected per animal at each time point.

FIGS. 3A-3B. A. phagocytophilum antibody responses in immunized C3H/HeN mice. A) A. phagocytophilum specific antibody responses in immunized mice were measured by IFA and titers expressed as the reciprocal of the highest dilution at which specific fluorescence was detected (B). Binding of antibodies specific to A. phagocytophilum was seen as defined red fluorescent inclusions (morulae) in infected HL-60 cells; in contrast similar fluorescent inclusions were not visualized using antibodies from negative control group V. Picture taken at 1:160 dilution of all antisera.

FIG. 4. A. phagocytophilum burden in immunized/challenged C3H/HeN mice blood. A. phagocytophilum growth kinetics in blood were measured by determining GE/μl based on the single copy gene msp5. GE/μl calculations were normalized based on the volume of blood collected per animal at each time point.

FIG. 5. Protection against A. phagocytophilum induced by immunization. A. phagocytophilum GE means plus standard deviations (error bars) at the peak of infection. 7 mice from each group were used for this analysis. The values that are significantly different from the values for the control group are indicated by asterisks *, p<0.05.

FIG. 6. 3 mice from the groups immunized with either VirB10 or ovalbumin control were sacrificed prior to challenge. Their antibody response was assayed by ELISA using intact A. phagocytophilum organisms attached to the ELISA plate. The values represent the average of duplicate readings from the three mice in either the VirB10 or control group. The data show the response of VirB10-immunized mice to whole organisms on the plate and suggest epitopes of VirB10 are surface-exposed and available to bind antibodies.

FIG. 7. CLUSTAL format alignment of VirB10s from multiple organisms by MAFFT (v7.220) (Amarginale_Virb, SEQ ID NO: 123; Aphagocytophilu, SEQ ID NO: 124; Echaffeenis_Vi, SEQ ID NO: 125; Eruminantium_Vi, SEQ ID NO: 126; Rtyphi_Virb10_C, SEQ ID NO: 127; Rprowazekii_Vir; SEQ ID NO: 128; Rconorii_VirB10; SEQ ID NO: 129; Rrickettsii_Vir, SEQ ID NO: 130; Otsutsugamushi_, SEQ ID NO: 131; and Ecoli_VirB10_3J, SEQ ID NO: 132).

BRIEF DESCRIPTION OF THE SEQUENCES

SEQ ID NO: 1: Sequence of VirB10 from A. phagocytophilum strain HZ.

SEQ ID NO: 2: Sequence of VirB9-1 protein from A. phagocytophilum strain HZ.

SEQ ID NO: 3: Sequence of VirB9-2 protein from A. phagocytophilum strain HZ.

SEQ ID NO: 4: Forward primer for amplification of DNA encoding Vir9B-1 protein.

SEQ ID NO: 5: Reverse primer for amplification of DNA encoding Vir9B-1 protein.

SEQ ID NO: 6: Forward primer for amplification of DNA encoding Vir9B-2 protein.

SEQ ID NO: 7: Reverse primer for amplification of DNA encoding Vir9B-2 protein.

SEQ ID NO: 8: Forward primer for amplification of DNA encoding VirB10.

SEQ ID NO: 9: Reverse primer for amplification of DNA encoding VirB10.

SEQ ID NO: 10: Forward primer for amplification of msp5 gene from A. phagocytophilum strain HZ for qPCR.

SEQ ID NO: 11: Reverse primer for amplification of msp5 gene from A. phagocytophilum strain HZ for qPCR.

SEQ ID NO: 12: Sequence of the qPCR probe for msp5 gene from A. phagocytophilum strain HZ.

SEQ ID NOs: 13 to 27: Sequences of antigenic peptides of VirB10.

SEQ ID NOs: 28-113: VirB10 sequences obtained from UniProt (web site: uniprot.org/uniprot).

SEQ ID NOs: 114-122: Sequences of PCR primers used to amplify VirB9-1, VirB9-2 and VirB10 and Taqman qPCR primers and probes used to quantify A. phagocytophilum load.

SEQ ID NOs: 123-132: Sequences of VirB10s from multiple organisms.

DETAILED DISCLOSURE OF THE INVENTION

Human granulocytic anaplasmosis (HGA) is a tick-borne disease caused by the etiologic agent A. phagocytophilum, a bacterium containing T4SS. HGA was designated as a nationally notifiable disease in the United States in 1998. HGA is described as a zoonosis since the pathogen infects humans as well as animals including dogs, cattle, sheep, deer, horses and rodents. Vaccines against HGA are not currently available and the currently available vaccines against other bacteria containing T4SS are not adequate. Thus, the subject application provides a component of T4SS as a vaccine against diseases caused by bacteria having T4SS, for example, A. phagocytophilum and methods of immunizing a host against an infection by a bacterium having T4SS. In some embodiments, outer membranes and fragments thereof that are obtained from bacteria having T4SS and which contain VirB10 are excluded as vaccine components in the methods of immunizing a host against infection by a bacterium having T4SS or as components of a vaccine.

In one embodiment, the invention provides a protein present in T4SS, for example, VirB10 or a fragment of VirB10, to immunize against an infection by a bacterium having T4SS, for example, A. phagocytophilum. In another embodiment, the invention provides a polynucleotide encoding VirB10 or a polynucleotide encoding a fragment of VirB10 to immunize against an infection by a bacterium having T4SS, for example, A. phagocytophilum. In particular embodiments, the VirB10 polypeptide comprises SEQ ID NO: 1.

Typically, T4SS is present in gram negative bacteria, such as Rickettsia spp., Ehrlichia spp., Helicobacter spp., Legionella spp., Bartonella spp., Brucella spp., and Anaplasma spp.

Non-limiting examples of the bacterial species containing endogenous T4SS include: Rickettsia typhi, Rickettsia prowazekii, Rickettsia rickettsia, Rickettsia conorii, Ehrlichia chaffeensis, Helicobacter pylori, Legionella pneumophila, Bartonella species, Anaplasma marginate, Anaplasma phagocytophilum, Ehrlichia ruminantium, Brucella species and Ehrlichia canis. Additional examples of bacterial species having T4SS and in which the invention can be practiced are well known to a person of ordinary skill in the art and such embodiments are within the purview of the invention. The subject invention can also provide protection against bacterial species that lack an endogenous T4SS system and which have been genetically manipulated to express T4SS.

In one embodiment, VirB10 of Anaplasma phagocytophilum or a fragment of VirB10 can be used to immunize a host against A. phagocytophilum infection. VirB10 in bacteria other than A. phagocytophilum can be identified based on sequence homology and such VirB10 or their fragments can be used in a vaccine to immunize against the infection by bacteria having T4SS. The following list provides non-limiting examples of UniProt entries for VirB10 proteins (each of which is hereby incorporated by reference in its entirety) in various bacteria having T4SS: A0A011QMA5 (SEQ ID NO: 28), A0A011TLZ5 (SEQ ID NO: 29), A0A021WBD5 (SEQ ID NO: 30), A0A021XC05 (SEQ ID NO: 31), A0A059FPP8 (SEQ ID NO: 32), A0A061Q3H1 (SEQ ID NO: 33), A0A063X2U5 (SEQ ID NO: 34), A0A068HFV0 (SEQ ID NO: 35), A0A069HMU4 (SEQ ID NO: 36), A0A070A750 (SEQ ID NO: 37), A0A071M5U1 (SEQ ID NO: 38), A0A073IY47 (SEQ ID NO: 39), A0A074MLS9 (SEQ ID NO: 40), A0A074TCY6 (SEQ ID NO: 41), A0A076G4V3 (SEQ ID NO: 42), A0A085AA72 (SEQ ID NO: 43), A0A085IIV0 (SEQ ID NO: 44), A0A090MT70 (SEQ ID NO: 45), A0A095CKP1 (SEQ ID NO: 46), A0A099QA58 (SEQ ID NO: 47), A0A0A0XLH7 (SEQ ID NO: 48), A0A0A1FHZ1 (SEQ ID NO: 49), A0A0A1IXK7 (SEQ ID NO: 50), A0A0A1PDK4 (SEQ ID NO: 51), A0A0A6W9W5 (SEQ ID NO: 52), A0A0B2BVJ6 (SEQ ID NO: 53), A0A0B2C1C1 (SEQ ID NO: 54), A0A0B5E2C6 (SEQ ID NO: 55), A0A0B7J1D9 (SEQ ID NO: 56), A0A0B7MV56 (SEQ ID NO: 57), A0A0C1ELG7 (SEQ ID NO: 58), A0A0C1MQK6 (SEQ ID NO: 59), A0A0D6GL13 (SEQ ID NO: 60), A0A0D6PK86 (SEQ ID NO: 61), A0A0D6QEJ3 (SEQ ID NO: 62), A1YBN8 (SEQ ID NO: 63), A3U3E8 (SEQ ID NO: 64), A3UHL6 (SEQ ID NO: 65), A3VIX9 (SEQ ID NO: 66), A3XDX0 (SEQ ID NO: 67), A5CFI6 (SEQ ID NO: 68), A7FCK5 (SEQ ID NO: 69), B2FJH5 (SEQ ID NO: 70), B4RHY3 (SEQ ID NO: 71), B6JK51 (SEQ ID NO: 72), B9JE62 (SEQ ID NO: 73), C3KFT1 (SEQ ID NO: 74), C6V5M2 (SEQ ID NO: 75), D3NTS2 (SEQ ID NO: 76), D5T6H3 (SEQ ID NO: 77), E0SJI8 (SEQ ID NO: 78), E5Y6Z7 (SEQ ID NO: 79), F0J7S0 (SEQ ID NO: 80), F4GMM5 (SEQ ID NO: 81), F7XVQ3 (SEQ ID NO: 82), H2ERZ5 (SEQ ID NO: 83), H9AY00 (SEQ ID NO: 84), I0EPK5 (SEQ ID NO: 85), I4MQG7 (SEQ ID NO: 86), I7F101 (SEQ ID NO: 87), J0B7G3 (SEQ ID NO: 88), J1IY73 (SEQ ID NO: 89), J8TK55 (SEQ ID NO: 90), K9P1S4 (SEQ ID NO: 91), L7SYL6 (SEQ ID NO: 92), N1MFN1 (SEQ ID NO: 93), Q0FXR1 (SEQ ID NO: 94), Q1LN34 (SEQ ID NO: 95), Q2K2E3 (SEQ ID NO: 96), Q2YJ81 (SEQ ID NO: 97), Q52SK2 (SEQ ID NO: 98), Q5EPB9 (SEQ ID NO: 99), Q69BE6 (SEQ ID NO: 100), Q8RPM1 (SEQ ID NO: 101), Q9A5M5 (SEQ ID NO: 102), Q9AGG7 (SEQ ID NO: 103), S2WS02 (SEQ ID NO: 104), S5YJB5 (SEQ ID NO: 105), S9QA92 (SEQ ID NO: 106), T0HQB6 (SEQ ID NO: 107), T0QH67 (SEQ ID NO: 108), T1XMT8 (SEQ ID NO: 109), U1H6S8 (SEQ ID NO: 110), V8QMP0 (SEQ ID NO: 111), X6JZV3 (SEQ ID NO: 112) and X7EE79 (SEQ ID NO: 113). A person of ordinary skill in the art can identify VirB10 in additional bacteria having T4SS and such embodiments are within the purview of the invention.

Accordingly, an embodiment of the invention provides a vaccine comprising an immunologically effective amount of VirB10 or a fragment of VirB10 and a pharmaceutically acceptable carrier and/or an adjuvant. Another embodiment of the invention provides a vaccine comprising an immunologically effective amount of a polynucleotide encoding VirB10 or a polynucleotide encoding a fragment of VirB10 and a pharmaceutically acceptable carrier and/or an adjuvant. For the purposes of this invention the term “immunologically effective amount” refers to the amount of VirB10 or a fragment of the VirB10 which elicits immune response in a host so that the host is protected from future infection caused by the bacterium in which VirB10 is present naturally (endogenously) or a bacterium genetically modified to express VirB10.

The term “endogenous” (and grammatical variations thereof) or the phrase “the bacterium in which VirB10 is present naturally” indicates that a particular VirB10 is a part of the T4SS present in the bacterium as the bacterium exists in nature, i.e., in the wild type bacterium.

In one embodiment VirB10, a fragment of VirB10, a polynucleotide encoding VirB10 or a polynucleotide encoding a fragment of VirB10 is labeled. The label can be designed for in vivo visualization of the protein, peptide or polynucleotide, for targeting the protein, peptide or polynucleotide to a specific tissue, organ or cell of the host, to increase the in vivo stability of the protein, peptide or polynucleotide or to increase immunogenicity of the protein or peptide.

Non-limiting examples of a label designed to visualize VirB10, a fragment of VirB10, a polynucleotide encoding VirB10 or a polynucleotide encoding a fragment of VirB10 include a fluorescent label, an enzyme label and a chromophore label. Additional examples of labels designed to visualize VirB10, a fragment of VirB10, a polynucleotide encoding VirB10 or a polynucleotide encoding a fragment of VirB10 are well known to a person of ordinary skill in the art and such embodiments are within the purview of the invention.

A label designed to target VirB10, a fragment of VirB10, a polynucleotide encoding VirB10 or a polynucleotide encoding a fragment of VirB10 to a tissue, organ or cell includes antibodies or fragments of antibodies or other biomolecules which specifically bind to one or more surface biomolecules present on the target tissue, organ or cell. The label can be designed to target, for example, Fc receptors, C-type lectins, complement receptors, major histocompatibility proteins, or other receptors present on the surface of dendritic cells or antigen presenting cells. Additional examples of suitable target biomolecules and corresponding binding biomolecules are well known to a person of ordinary skill in the art and such embodiments are within the purview of the invention.

A label designed to increase the in vivo stability or immunogenicity of VirB10 or a fragment of VirB10 includes tripalmitoyl-S-glyceryl cysteine, polylysine core, carbohydrate, N-pyroglutamate, amide group on the C terminus, acetyl group, glycosyl group, lipid group, unnatural amino acids, peptidomimetics, peptide carriers and polyethylene glycol (PEG). Non-limiting examples of labels that increase the in vivo stability or immunogenicity of VirB10 or a fragment of VirB10 are discussed in Goodwin et al. The contents of Goodwin et al. are herein incorporated by reference in their entirety. Additional examples of labels which can increase the in vivo stability or immunogenicity of VirB10 or a fragment of VirB10 are well known to a person of ordinary skill in the art and such embodiments are within the purview of the invention.

In one embodiment, VirB10 or a fragment of VirB10 is modified to increase its in vivo stability. Non-limiting examples of modifications which increase the in vivo stability of VirB10 or a fragment of VirB10 include incorporation of non-natural amino acids, pseudo-peptide bonds and cyclization. Additional examples of modifications that increase the in vivo stability of VirB10 or a fragment of VirB10 are also described in Goodwin et al. and Gentilucci et al. The contents Goodwin et al. and Gentilucci et al. are herein incorporated by reference in their entirety. Additional examples of modifications which can increase the in vivo stability of VirB10 or a fragment of VirB10 are well known to a person of ordinary skill in the art and such embodiments are within the purview of the invention.

An embodiment of the invention provides a vaccine comprising a fragment of VirB10 or a polynucleotide encoding a fragment of VirB10 and a pharmaceutically acceptable carrier and/or an adjuvant, wherein the fragment elicits an immune response in a host and the host is immune to a future infection caused by the bacterium in which the particular VirB10 is present naturally. The fragment of VirB10 used in the vaccines of the invention can comprise about 5 to about 50, about 10 to about 40, about 15 to about 30, about 20, about 10 or about 5 amino acids.

In one embodiment, the fragment of VirB10 is selected from the fragments provided in Table 1. In another embodiment, the VirB10 fragment or VirB10 polypeptide can be fused to a heterologous sequence, such as a carrier protein (e.g., bovine serum albumin, keyhole limpet hemocyanin, ovalbumin or other carrier protein used to stimulate an immune response to peptides).

TABLE 1 Examples of fragments of VirB10 protein used in the vaccines of the invention. Start End Position in Position SEQ SEQ ID in SEQ ID NO NO: 1 Sequence ID NO: 1 13 16 DNVNVVGVAKSKKLFVIIVVLIATGLMYYFF 46 14 85 APRILTPPPRLPELPPLVMPTVPDIPVVTKLLKP 118 15 147 EISLPLPYK 155 16 214 QSPSVRA 220 17 227 RYIILQG 233 18 235 MIDAVLET 242 19 247 DISGVLRAVVSRDVYASSGDAVVIPKG 273 20 275 RLIGSYFF 282 21 289 VRVDVNWSRVILPHGVDIQIA 309 22 321 ISGVVDN 327 23 329 VGSILTSTIFLAGISLGTAYVTEQIPS 355 24 357 RTETVKVET 365 25 376 TSSSLSTKIVSD 387 26 407 TPTVYVDQ 414 27 416 TVMKVFVNQDVVFP 429

The vaccine of the invention can be formulated using adjuvants, emulsifiers, pharmaceutically-acceptable carriers or other ingredients routinely provided in a vaccine. Optimum formulations can be readily designed by one of ordinary skill in the art and can include formulations for immediate release and/or for sustained release, and for induction of systemic immunity and/or induction of localized mucosal immunity (e.g, the formulation can be designed for intranasal, intravaginal or intrarectal administration).

Guidelines for designing optimal vaccines can be found in Brito et al., Avanti and Li et al. The contents of Brito et al. are herein incorporated by reference in their entirety, particularly, page 132, Table 1; page 133 under immune potentiator adjuvants; page 133-136 under aluminum salt adjuvants; page 136-139 under emulsions; 139-140 under liposomes as adjuvants; page 140-141 under PLG particulate delivery systems; and page 141 under alternate particulate systems. The contents of Avanti et al. are also herein incorporated by reference in their entirety, particularly Chapters 1, 2 and 7. Further, the contents of Li et al. are herein incorporated by reference in their entirety, particularly pages 521-527 under Particulate Peptide Vaccine Delivery Methods.

The vaccine disclosed herein can be formed with a pharmaceutically acceptable carrier such as a phosphate buffered saline, a bicarbonate solution, or an adjuvant to produce a pharmaceutical composition. The carrier must be “acceptable” in the sense that it is compatible with the active ingredient of the composition, and preferably capable of stabilizing the active ingredient and not deleterious to the subject to be treated. The carrier is selected on the basis of the mode and route of administration and standard pharmaceutical practice. Suitable pharmaceutical carriers and diluents, as well as pharmaceutical necessities for their use, are described in Remington's Pharmaceutical Sciences.

In one embodiment, the antigen is mixed with an adjuvant to form a composition useful for immune modulation. This composition may be prepared as injectable, as liquid solutions or as emulsions. See U.S. Pat. Nos. 4,601,903; 4,599,231; 4,599,230; and 4,596,792. An “adjuvant” refers to a substance added to an immunogenic composition, such as a vaccine, that, while not having any specific antigenic effect in itself, can stimulate the immune system and increase the immune response to the immunogenic composition. Examples of adjuvants include, but are not limited to, alum, alum-precipitate, Freund's complete adjuvant, Freund's incomplete adjuvant, monophosphoryl-lipid A/trehalose dicorynomycolate adjuvant and water in oil emulsions.

A further embodiment of the invention provides a method of immunizing a host against an infection by a bacterium having T4SS, the method comprising administering to the host a vaccine comprising a pharmaceutically effective amount of VirB10, a fragment of VirB10, a polynucleotide encoding VirB10 or a polynucleotide encoding the fragment of VirB10 and a pharmaceutically acceptable carrier and/or an adjuvant.

The method of the invention can be used to immunize a host, for example, a mammal, against an infection by a bacterium having the T4SS. Non-limiting examples of mammals in which the methods of the invention can be practiced include dogs, cats, pigs, cattle, rabbits, sheep, goats, deer, horses, rodents and humans. Additional examples of hosts in which the methods of the invention can be practiced are well known to a person of ordinary skill in the art and such embodiments are within the purview of the invention.

In one embodiment, the invention provides a method of immunizing a host against an infection by a bacterium containing T4SS, wherein the method comprises administering to the host a vaccine comprising VirB10, a fragment of VirB10, a polynucleotide encoding VirB10 or a polynucleotide encoding the fragment of VirB10 and a pharmaceutically acceptable carrier and/or an adjuvant, and wherein the bacterium is a member of Rickettsia spp., Ehrlichia spp., Helicobacter spp., Legionella spp., Bartonella spp., Brucella spp., and/or Anaplasma spp. In certain embodiments, the bacterium is Rickettsia prowazekii, Rickettsia rickettsia, Rickettsia conorii, Ehrlichia chaffeensis, Helicobacter pylori, Legionella pneumophila, a Bartonella species, a Brucella species (e.g., Brucella abortus), Anaplasma marginate, Anaplasma phagocytophilum, Ehrlichia ruminantium or Ehrlichia canis.

The vaccine of the invention can be administered by any convenient route including subcutaneous, intradermal, intranasal, oral, intramuscular, intraperitoneal, or other parenteral or enteral route. A person of ordinary skill in the art can identify a particular route of administration suitable for a particular host and a given bacterium and such embodiments are within the purview of the invention.

VirB10, a fragment of VirB10, a polynucleotide encoding VirB10 or a polynucleotide encoding a fragment of VirB10 can be administered as a single dose or multiple doses. Optimum immunization schedules can be readily determined by the ordinarily skilled artisan and can vary with parameters, for example, age, weight and species of the host, the type of vaccine composition and the bacterium against which immunization is desired and such embodiments are within the purview of the invention.

An embodiment of the invention provides a method of immunizing a host against an infection by a bacterium having T4SS, wherein the immunization is performed according to prime boost immunization. For the purpose of this invention, the phrase “prime boost immunization” indicates that the VirB10, a fragment of VirB10, a polynucleotide encoding VirB10 or a polynucleotide encoding a fragment of VirB10 is administered in a plurality of doses. As such, the immune system of a host encounters multiple exposures to VirB10, a fragment of VirB10, a polynucleotide encoding VirB10 or a polynucleotide encoding a fragment of VirB10, which results in a stronger immune response compared to single administration of the vaccine. Certain examples of prime boost immunizations are discussed in Woodland et al., the contents of which are herein incorporated by reference in their entirety.

In one embodiment, the prime boost immunization comprises administering a pharmaceutically effective amount of a polynucleotide encoding VirB10 or a polynucleotide encoding a fragment of VirB10 followed by administering a pharmaceutically effective amount of VirB10 or a fragment of VirB10. In another embodiment, the prime boost immunization comprises administering a pharmaceutically effective amount of VirB10 or a fragment of VirB10 followed by administering a polynucleotide encoding VirB10 or a polynucleotide encoding a fragment of VirB10.

In certain embodiments, the interval between the administration of the polynucleotide and the protein or a fragment of the protein is about 1 week to about 4 weeks, about 2 weeks to 3 weeks, 2 to 4 weeks, or about 2 weeks. In another embodiment of the invention, the vaccine is administered in the form of a “cocktail” that contains at least two polynucleotides or at least two peptides. The cocktail can also contain a mixture of a polynucleotide and a peptide.

All patents, patent applications, provisional applications, and publications referred to or cited herein are incorporated by reference in their entirety, including all figures and tables, to the extent they are not inconsistent with the explicit teachings of this specification.

Following are examples which illustrate procedures for practicing the invention. These examples should not be construed as limiting. All percentages are by weight and all solvent mixture proportions are by volume unless otherwise noted.

Example 1—Preparation of Soluble Recombinant VirB9-1, VirB9-2 and VirB10S

The open reading frames of A. phagocytophilum virB9-1, virB9-2 and virB10 genes were amplified by PCR (Table 2) and the purified products cloned into a DNA vaccine vector and the pET101/D-TOPO directional expression system. Recombinant constructs were purified and sequences were confirmed by PCR and DNA sequencing. The pET101 constructs were re-transformed into E. coli BL21 Star (DE3) cells and induced to express with 0.5 mM IPTG and growth in M9 minimal media supplemented with 50 μg/ml carbenicillin and 1% glucose. Expression of recombinant VirB9-1, Vir9-2 and VirB10 was verified by SDS-PAGE followed by Western blot analyses using His₆-tagged monoclonal antibody (FIG. 1). 500 ml of IPTG-induced cultures were processed and soluble fractions containing the recombinant His₆-tagged fusion proteins were purified using low-density Nickel agarose bead columns. Eluted protein was concentrated using Centricon Plus-70 centrifugal filter units, and concentration determined using a Qubit protein assay kit. The recombinant proteins were run on a SDS-PAGE gel to confirm purity.

For preparation of the DNA vaccine, the VirB9-1, VirB9-2, and VirB10 were separately amplified by PCR and cloned into the vector pcDNA3.1/CT-GFP-TOPO (Invitrogen). This vector provides the CMV (cytomegalovirus) promoter 5′ to the inserted gene for constitutive expression in mammalian cells and the GFP (Green Fluorescent Protein) gene 3′ to the inserted gene. The validity of the constructs was checked prior to use in immunizations by sequencing the gene insert and junction regions and by transfecting RF6A endothelial cells with isolated plasmid DNA to verify GFP expression by fluorescence. For preparation of immunizing plasmid DNA, bacteria were grown in LB/Ampicillin 100 μg/ml. The ZR Plasmid Gigaprep kit (Zymo Research) was used to isolate endotoxin-free plasmid DNA from the bacterial pellets. The yields of DNA obtained were: TOPO-GFP (control, no inserted gene): 6 liters of culture gave ˜6.5 mg; VirB 9-1 plasmid: 6 liters of culture gave 29 mg; VirB 9-2 plasmid: 6 liters of culture gave ˜19 mg; and VirB10 plasmid: 4 liters of culture gave ˜23 mg.

The culture and purification conditions described above were optimized to produce adequate yields of soluble recombinant VirB9-1, VirB9-2 and VirB10. For protein expression the temperature was reduced to 4° C. to avoid protein aggregation and reduction of heat shock proteases that could promote inclusion body formation, cellular toxicity and high levels of protein degradation. Additionally, modification of nutrient media was employed to avoid excess bacterial growth and depletion of substrates and cofactors. This resulted in the isolation of soluble recombinant VirB9-1, VirB9-2 and VirB10s (FIG. 1) suitable for use in the immunization experiments.

TABLE 2 PCR primers used to amplify VirB9-1, VirB9-2 and VirB10 and Taqman qPCR primers and probes used to quantify A. phagocytophilum load. Target Size PCR AB1703 CACCATGAGCACAAATATTGGCGTACCAG (SEQ virB9-1  769 bp ID NO: 114) AB1704 ACTAAGAGCCTGATTCACAACTTCTACACTCCTGC (SEQ ID NO: 115) AB1705 CACCATGGCTGATGATCACATTAAGACCTTGAAC virB9-2  736 bp (SEQ ID NO: 116) AB1706 TTTCCGGCGTCTTTCAGCACCCTTC (SEQ ID NO: 117) AB1707 CACCATGGCTGACGAAATAAGGGGTTCTAG (SEQ virB10 1306 bp ID NO: 118) AB1708 CCTCACCGCATCACGAGGAAATACTACG (SEQ ID NO: 119) qPCR AB1334 AGATGCTGACTGGGGATGAG (SEQ ID NO: 120) msp5  125 bp AB1335 TCGGCATCAACCAAGTACAA (SEQ ID NO: 121) *AB1336 CGTAGGTGAGTCTGATAGTGAAGG (SEQ ID NO: 122) *Oligonucleotide labeled with Hexachloro-fluorescein (HEX) at the 5′ end and Tetramethylrhodamine TAMRA at the 3′ end

Example 2 —A. Phagocytophilum Infection Kinetics in Different Mouse Strains

Three different mouse strains (C57BL/6, C3H/HeN, and Balb/C) were tested to evaluate A. phagocytophilum infection kinetics and to select an appropriate mouse strain for A. phagocytophilum infection for immunization and challenge experiments. Two C57BL/6, two C3H/HeN and two Balb/C mice were inoculated with isolated organisms from 5.22×10⁵ infected HL-60 cells (>90% infection). DNA extracted from blood collected every other day over 24 days was used to determine the A. phagocytophilum load by measuring the increase in the number of genome equivalents (GE) using qPCR with primers and probes that target the single copy gene msp5 (Table 2). Ten-fold serial dilutions of the NY18E2/pCR-TOPO plasmid carrying the msp5 gene were used for standard curve preparation, and the msp5 gene copy numbers were calculated based on the standard curve.

Results showed that C3H/HeN and Balb/C mice are susceptible to A. phagocytophilum (human HZ strain) infection as shown by an increase of GE in blood at 8 days post-infection for C3H/HeN mice (average of 705 GE/μl of blood) and between 6 and 8 days post-infection in Balb/C mice (average of 636 GE/μ1 of blood) (FIG. 2). In contrast, in C57BL/6 mice, only mouse #2 presented a minor increase of up to 150 GE/μl of blood at day 6 post-infection indicating that this strain better controlled A. phagocytophilum infection. During the course of infection, a relapse peak of infection was detected after 16 days post-infection in both C3H/HeN and Balb/C strains suggesting a possible chronic infection. C3H/HeN strain was selected to determine mouse response to immunization with DNA vaccine followed by a recombinant protein vaccine encoding VirB9-1, VirB9-2 and VirB10 because the results presented here support previous work which indicate that C3H/HeN is a good model for A. phagocytophilum infection.

Immunization and Challenge of C3H/HeN

5 groups of 10 mice were vaccinated in a prime boost fashion with plasmid DNA immunization followed by recombinant proteins as described in Table 3.

TABLE 3 C3H/HeN mice immunization schedule. Group Immunogen Dosage Amount I virB9-1 plasmid 2 100 μg 2 week intervals rVirB9-1 protein 2 100 μg 2 week intervals II virB9-2 plasmid 2 100 μg 2 week intervals rVirB9-2 protein 2 100 μg 2 week intervals III virB10 plasmid 2 100 μg 2 week intervals rVirB102 protein 2 100 μg 2 week intervals virB9-1 plasmid, 2 100 μg/ 2 week intervals virB9-2 plasmid, plasmid virB10 plasmid IV virB9-1, rVirB9- 2 100 μg/ 2 week intervals 2, rVirB10 protein Empty TOPO- 2 100 μg 2 week intervals GFP V Ovalbumin 2 100 μg 2 week intervals

Two weeks after the last immunization, three mice were randomly selected for serum collection and for isolation of spleen and lymph nodes from each group. Preliminary serological work was performed using immunofluorescence assay (IFA) to determine how the immunized mice reacted to whole A. phagocytophilum organisms and to measure antibody titers. Antigen slides were prepared from A. phagocytophilum/HZ infected HL-60 cells. Sera from the three mice in each group were combined and serially diluted starting from 1:80 up to 1:81920. Ten microliters of serum was applied to each well with duplicates for each dilution and incubated for 1 hour at room temperature in a humidified chamber. After incubation the serum was removed and the slides washed five times for 5 minutes. Ten microliters of Alexa fluor 568-Goat anti-mouse IgG antibody at a dilution of 1:1600 was applied to each well and incubated for 1 hour at room temperature. The slides then were washed as described above and mounted with ProLong Gold antifade reagent with DAPI (4′,6-diamidino-2-phenylindole) (FIG. 3). IFA analysis showed that higher titers of antibodies against A. phagocytophilum were detected in the serum of vaccinated animals (Groups I through IV), compared to negative control mice (Group V) vaccinated with Empty TOPO-GFP/Ovalbumin (FIG. 3).

Protection against A. phagocytophilum induced by virB9/VirB9, virB9-2/VirB9-2, and virB10/VirB10 was evaluated. 35 immunized mice (7 mice/group) were challenged with one dose of isolated organisms from 5.63×10⁵ HL-60 infected cells (>90% infected) and the bacterial burden in the blood of each mouse was measured by real time qPCR targeting the single copy gene msp5 to determine the number of A. phagocytophilum GE as described above. On day 8, the bacterial load in the blood ranged from 451 GE/μl up to 1267 GE/μl in the mice in Group I, from 358 GE/μl up to 2188 GE/μl in Group II, from 396 GE/μl up to 980 GE/μl in Group III, from 118 GE/μl up to 2225 GE/μl in Group IV and from 607 GE/μl up to 2988 GE/μl in negative control Group V (FIG. 4). However real time qPCR did not detect any A. phagocytophilum GE in one mouse from Group I, or in two mice from Group III. Although the bacterial load in Groups I, II and IV was lower than in Group V, these differences were not significant. In contrast, there was a significant difference between the bacterial load in Group III when compared with Group V (p=0.032).

These results indicate that immunized mice (pre-challenge) with VirB9, VirB9-2, VirB10 and the mixture of VirB9-1, VirB9-2 and VirB10 developed antibodies that reacted with A. phagocytophilum. However real-time qPCR of DNA extracted from the blood of the challenged mice showed that the bacterial load was significantly lower only in Group III when compared to the negative control mice in Group V. Such an result was not expected in view of the antibody titers observed in the Group II and Group IV mice and in view of the Group IV animals that were immunized (primed and boosted) with a mixture of VirB9-1, VirB9-2 and VirB10 (see Table 3 and FIG. 3).

It should be understood that the examples and embodiments described herein are for illustrative purposes only and that various modifications or changes in light thereof will be suggested to persons skilled in the art and are to be included within the spirit and purview of this application and the scope of the appended claims. In addition, any elements or limitations of any invention or embodiment thereof disclosed herein can be combined with any and/or all other elements or limitations (individually or in any combination) or any other invention or embodiment thereof disclosed herein, and all such combinations are contemplated within the scope of the invention without limitation thereto.

REFERENCES

-   1. Brito et al. (2013), Vaccine adjuvant formulations: A     pharmaceutical perspective, Seminars in Immunology, 25:130-145. -   2. Avanti (2012), Innovative strategies for stabilization of     therapeutic peptides in aqueous formulations (Doctoral     Dissertation), project D6-202 of the Dutch Top Institute Pharma. -   3. Li et al. (2014), Peptide Vaccine: Progress and Challenges,     Vaccines, 2:515-536. -   4. Woodland et al. (2004), Jump-starting the immune system:     prime-boosting comes of age, TRENDS in Immunology, 25(2):98-104. -   5. Goodwin et al. (2009), Peptides as therapeutics with enhanced     bioactivity, Current Medicinal Chemistry, 19:4451-4461. -   6. Yang et al. (2009), An introduction to epitope prediction methods     and software, Reviews in Medical Virology, 19: 77-96. -   7. Gentilucci et al. (2010), Chemical modifications designed to     improve peptide stability: Incorporation of non-natural amino acids,     pseudo-peptide bonds, and cyclization, Current Pharmaceutical     Design, 16:3185-3203. 

We claim:
 1. A method of immunizing a host against an infection by a bacterium having Type 4 secretory system (T4SS), the method comprising administering an effective amount to the host an immunogenic composition comprising an immunological Iv effective amount of a T4SS protein conjugated to a carrier protein and a pharmaceutically acceptable carrier and/or an adjuvant; wherein the T4SS protein consists of VirB10 of Anaylasma phagocytophilum, and wherein the bacterium is Anaplasma phagocytophilum.
 2. The method of claim 1, wherein the carrier protein is keyhole limpet hemocyanin, ovalbumin or bovine serum albumin.
 3. The method of claim 1, wherein VirB10 is cyclized or comprises SEQ ID NO:
 1. 